1. Field of the Invention
The present invention relates to a heat treatment apparatus for a laminated body of nanocrystal alloy ribbon used for magnetic heads, transformers, choke coils, etc., or particularly, for amorphous alloy ribbon having low iron loss and coercive force and excellent soft magnetic properties, and a lamination jig thereof, as well as a soft magnetic core acquired by a heat treatment of an Fe-based amorphous alloy.
2. Description of the Related Art
A laminated body of amorphous alloy ribbon is used as a soft magnetic core in magnetic heads, transformers, choke coils, etc. Additionally, since an Fe-based nanocrystal alloy is a soft magnetic material capable of satisfying both a high saturation magnetic flux density and a low coercive force, the amorphous alloy ribbon is recently heat-treated and used as a laminated body.
The Fe-based nanocrystal alloy is an alloy containing Fe as a main element that is an essential element responsible for magnetism. In manufacturing of a soft magnetic core using this Fe-based nanocrystal alloy, it is necessary to laminate a ribbon of an alloy composition having an amorphous structure to form a core, and to apply a heat treatment to the core so as to precipitate fine bcc-Fe crystals. It is noted that Bcc stands for a body-centered cubic lattice structure.
However, when bcc-Fe crystals are precipitated by the heat treatment, an excessive temperature rise occurs due to self-heating associated with the crystallization of the bcc-Fe crystals, resulting in a problem of occurrence of the enlargement of crystal grains of the bcc-Fe crystals and the deterioration in soft magnetic properties due to precipitation of an Fe compound such as Fe—B and Fe—P.
The countermeasures to the conventional problem described above include terminating a first heat treatment to a quenched body mainly composed of Fe in the amorphous phase when heat generation associated with the crystallization of the bcc-Fe crystals starts, and applying a second heat treatment after the end of the heat generation of the crystallization (see, e.g., Japanese Patent Publication No. 2003-213331). As a result, fine bcc-Fe crystals are precipitated. The quenched body mainly composed of Fe mainly in the amorphous phase is acquired by quenching a high temperature liquid metal mainly composed of Fe.
The countermeasures to the conventional problem described above include providing an endothermic reactant on at least one surface of amorphous alloy ribbon (see, e.g., Japanese Patent Publication No. 2015-56424). The endothermic reactant has an endothermic reaction temperature between a first crystallization temperature at which the heat generation due to crystallization of bcc-Fe of the amorphous alloy ribbon starts and a second crystallization temperature at which the heat generation due to crystallization of the Fe compound starts. The excessive temperature rise is suppressed by disposing the endothermic reactant as described above before performing the heat treatment.
FIGS. 6A and 6B are views of an example of a method of manufacturing a conventional soft magnetic core described in Japanese Patent Publication No. 2015-56424. FIG. 6A is a perspective view of a soft magnetic core 601 before heat treatment acquired by toroidally-winding and laminating an amorphous alloy ribbon having a layer of an endothermic reactive material formed on one surface. FIG. 6B is a partially enlarged cross-sectional view taken along a plane A of FIG. 6A, and a layer of an endothermic reactant 603 is formed on one side of an amorphous alloy ribbon 602 so that the endothermic reactant 603 and the amorphous alloy ribbon 602 are alternately arranged by laminating the amorphous alloy ribbon 602.
In Japanese Patent Publication No. 2003-213331, it is described that in a method of detecting a start time point of self-heating due to crystallization of bcc-Fe crystals, the start time point can be detected by successively measuring an ambient temperature inside a heat-treating furnace and a temperature of a core of a laminated alloy composition having an amorphous structure at the same time to detect a time point at which a rate of increase in the temperature of the core becomes higher than a rate of increase in the ambient temperature.
However, since it is not practical to measure the core temperature of all the cores housed in the heat-treating furnace in consideration of the manufacturing cost, the cores must be limited in terms of the measurement of temperature. Therefore, the start time point of self-heating due to the crystallization of the bcc-Fe crystals varies in individual cores depending on a temperature condition according to a location in the furnace, a rate of temperature rise in the heat-treating furnace, or a size of a core, a variation in composition at the time of manufacturing of a core, etc. Thus, the temperature measurement of the limited cores results in deviation also in detection, and a delay occurs in the timing of stopping the temperature rise in some cores and leads to precipitation of an Fe compound because of overheating due to self-heating associated with crystallization, resulting in a problem of degradation in soft magnetic properties.
Even if the temperature rise is stopped by detecting the self-heating due to crystallization of bcc-Fe crystals, a time delay occurs before the furnace temperature drops. Therefore, the temperature rise due to self-heating continues for a while and, in the case of an amorphous alloy composition having a small difference between the bcc-Fe crystallization temperature (first crystallization temperature) and the crystallization temperature of the compound such as Fe—B (second crystallization temperature), the temperature inside the core exceeds the crystallization temperature of the Fe compound and the precipitation of the Fe compound results in a problem of degradation in soft magnetic properties.
In the configuration in Japanese Patent Publication No. 2015-56424, it is described that an endothermic reactant is disposed on at least one surface of the amorphous alloy ribbon to absorb self-heating associated with crystallization; however, since the disposition of the endothermic reactant reduces the space factor of the amorphous alloy ribbon relative to the core volume, the configuration has a problem of deterioration in the soft magnetic properties of the core.